Signaling system



Sept. 26, 1939.

K] H. THUNELL Er Al. 2,174,371

A SIGNALING SYSTEM Nov. 5, ll

4 Sheets-Sheet l WW1 ATTN- 4 Sheets-Sheet 2 Karl HllrrlThUFeH S'en Dan e\ Wren Per Hurr Elm @mesma lNvENTor s BH AML TLM', ATTV.

K. H. THUNELL er AL SIGNALING SYSTEM Filed Nov. 5, 195e Sept. 26, 1939.

Sept. 26, 1939.

K. H. THUNELL El' AL SIGNALING SYSTEM Filed Nov. 5, 1938 4 Sheets-Sheet 3 Sept. 26, 1939.

K. H. THUNELL ET AL 2,174,371

. SIGNALING SYSTEM Filed Nov. 5, 1938 4 Sheets-Sheet 4 Karl Hun( Thvnell S+enDum \V\ Yen Psv Harri.) Elms Claessen mwENTO 6 5 l ll Patented Sept. 2.6, 1939 UlTEl STES rare SIGNALING SYSTEM Karl Harry Thunell, Sten Daniel Vigrcn, and Per Harry Elias Claessen, Stockholm, Sweden i4 Claims.

The present invention relates to new and usei'ul improvements in the transmission of pulsating direct current signals in both directions over inductively connected electric circuits.

The invention refers particularly to circuits in telephone, telegraph and signaling systems of the type using trunk lines for two-way trahie between exchanges or stations.

The invention is particularly suitable for the transmission of signals over junction or trunk lines and even over long distance lines between two automatic telephone exchanges in the same city or between two stations or exchanges situated in cities far apart, said trunk or long dis tance lines consisting ci side and/or phantom circuits, the sections of which are inductively connected by repeating coils and/or transformers, whereby signals and operating impulses of diiierent kinds can be transmitted in both directions over the same trunk line.

Heretofore junction lines between automatic telephone exchanges in the same city have not been phantomised, due to the fact that it has not been possible in an eliicient and simple way to pass definite direct current signal impulses of any desired direction over inductively connected circuits.

By using the new system according to this invention a great saving in the operating expenses can be made, due to the fact that by phantor-.iisn ing existing junction or trunk lines a new phantom trunk circuit is obtained for every two existing physical metallic circuits, whereby dialing can be performed and controlling signal impulses can be sent over all such side and phantom circuits.

Junction lines and trunk lines inductively connected and arranged for the transmission of signals in both directions are known, whereby balancing and connecting means have been arranged in such a way that signals and operating impulses to a certain extent can be transmitted and received. Such balancing means comprise, however, complicated connection arrangements and have, besides, the disadvantage that they generally must be adjusted to the exact length and to the special qualities of each individual trunk line.

Many propositions have been made to solve the problem of transmitting signals over an inductively connected trunkline with the associated transformers, etc., which signals could be sent and received under all possible circumstances, for instance: Transmission in a certain direction immediately after a transmission in the opposite direction; simultaneous transmission in both di rections; transmission in one direction immediately after a transmission in both directions simultaneously, etc.

The problem has, however, not been solved in a satisfactory way. The balance of a trunk line can only be exactly alike, if same currents pass 5 through. the balancing networks and through the line. These requisites have, however as yet not been fuliilled by known methods for all current magnitudes. It thus been proposed to make the primary ci line transformer connectable to 10 one and/ or to the other pole of a current source, in such way that a current oi a certain direction closed through the primary of said line transformer, whereby a current impulse of, for instance, positive direction is generated in the l5 secondary of the line transformer and transmitted over the line. A current impulse of opposite or negative direction is obtained in similar manner when a current passing through the said primary is interrupted, as for instance described in the German Patent No. 581,559 and the British Patent No. 395,719. Said arrangements have, however, certain important inconveniences, the elimin nation of which is the principal object of this invention. 25

In the known circuits the primaries of the line transformers are not permanently connected to the line, and therefore disturbing noises can be heard in telephone receivers eventually connected to the station or exchange circuits, when the primary of said transformers are connected to or disconnected from the station circuits. Said line transformers will furthermore be exposed to permanent magnetising currents or to direct currents which fo relatively long periods of time are passing through the primaries of said transformers. These circumstances represent a serious inconvenience to the transmission of voice currents for which said line transformers primarily are intended. 40

The battery voltages generally available in telephone exchanges are besides too low to be directly usable for such a direct transmission of current impulses. At least is this the oase when long distance lines are involved. Auxiliary batteries or other extraordinary arrangements must in such a case be available. It might also be possible to so dimension the line transformers that the line voltages are suiiioiently raised to overcome the said inconveniences, but in such a case a serious decrease of the transmission efiiciencies of the transformers with respect to` the voice currentswould be experienced.

There have been great difficulties hitherto in transmitting current signal impulses of any desired sequence of direction over trunk lines inductively connected, because only a limited number of different types of signals could be transmitted with any satisfactory degree of security and in such a manner that each signal type could be entirely interpretable at respective stations.

These inconveniences have been particularly noticeable on inductively connected trunk lines between automatic telephone exchanges, between which a plurality of different signal types must be transmitted.

The object of the present invention is to eliminate all these previously experienced difficulties and facilitate the transmission in any direction of a plurality of types of signals of any sequence of polarity over a trunk line.

This object is `generally accomplished in a transmitting system comprising the simultaneous transmission of signals in both directions over a trunk line by means of pulsating currents of any desired sequence of polarity, two stations, each thereof comprising a direct current source, transmitting, receiving and connecting means permanently and inductively connecting said stations and said transmitting and receiving means to said trunk line, balancing means associated with said transmitting and receiving and connecting means, said balancing, receiving and connecting means being provided with substantially constant magnetic and electrical characteristics, whereby interferences between transmitted and received signals at any normally transmitted current magnitude at any of the stations is impeded.

Such a trunk line with balancing, receiving and connecting means of substantially constant magnetic and electrical characteristics can be obtained in several different ways without changing the scope of the invention, so that these characteristics cannot be changed when transmission takes place at either of the stations.

One of these ways consists in constructing the line transformers associated with the balancing and receiving means in such a way that magnetic hysteresis phenomena, remanent magnetism and the like, which might vary the magnetic properties of a transformer and thereby the electric balance of the corresponding receiving and transmitting circuits, are eliminated.

If balancing means are used, for instance, by differential windings on the receiving relay in combination with a line transformer, or if a differential line transformer is used instead of an ordinary transformer with single windings, the current passing through said balancing differential windings will be substantially constant.

In order to make clear what really takes place in an ordinary transformer used as connecting means to a line, over which, apart from signals in one or in the other direction, also simultaneous transmission of signals in both directions takes place, the following explanation is given:

When transmission of pulsating current signals takes place in both directions simultaneously over a line inductively connected by means of a normal transformer to the end stations, the pulsating current through the line and the windings of such a transformer can be either double the amount of that passing in one direction, when the current impulses from both stations are of the same direction on the line, or said currents can be zero, when two opposed current impulses meet on the line.

Furthermore, the inductance of an ordinary transformer in magnetised condition can often be ten-fold to that in non-magnetised condition,

on account of violent fluctuations in the remanent magnetism existing in the magnetic circuit of said transformer.

From above explanations it is readily understood that equal currents ordinarily passing through a balancing network of a station and the line when transmission takes place in one direction only, do not longer exist after the transmission of one or more current signal impulses in both directions simultaneously. Due to said circumstances the impedances of the balancing networks and that of the line are not alike any more, when a current impulse is transmitted in one direction only immediately after said simultaneous transmission in both directions.

The above difficulties can according to this invention preferably be solved by arranging the transmitting, receiving, balancing and line connecting circuits in such a way that the magnetic and electric properties of said circuits are not iniiuenced by the transmission of signals in one and/or other direction.

The circuits can according to this solution be arranged according to Figures l, 5 and 7.

Another solution which can be used consists in using line signal transformers of substantially constant inductance, obtained by the use of a material in the magnetic circuits of said transformer of high initial and relatively constant permeability for normal induction intensities of the magnetic eld, produced by said pulsating currents, whereby a substantially constant inductance of the said line transformers is maintained for any normally transmitted current signal magnitude.

By using such a magnetic circuit the balance between the balancing network and the line is not disturbed for varying remanent elds. To obtain these desirable features the transformer laminations or magnetic material should be such a material which gives a permeability curve of high initial value and then remains substantially constant up to maximum magnetisation prevailmg for the corresponding magnetic elds. Some examples of material suitable for such a purpose are here mentioned:

(a) Ternary alloys of iron, silicon and. aluminium in the range 6-11% Si and 4-8% Al have been shown to have high initial permeability with its maximum initial value of 35,100 at 9.62% of Si and 5.38% of Al with a maximum permeability of 117,500 and its hysteresis loss 28 ergs/cm.3 per cycle, the coercive force being 0.022 oersted, the residual magnetic induction being 3350 gausses and maximum induction being about 10,000 gausses.

(b) Alloys of ironnickel-coppermolybdenum in the range of 72% Ni, 11%Fe, 14% Cu and 3% Mo. This alloy has an initial permeability of about 40,000; a maximum permeability of about 100,000 for a maximum magnetic intensity of 5000 to 6000 gausses and a magnetic force up to about 0.5 oersted.

The desired qualities of the line signal transformer can also be obtained by using ordinary iron, providing the magnetic circuit with small air gaps, or by using compressed iron powder. In order to obtain magnetising currents of sufciently low values a great number of windings have, however in this case, to be used, causing large dimensions of the transformer, this solution therefore being less desirable.

In order that line signal transformers provided with ordinary iron nuclei may be given small dimensions, a balancingy inductance (choke coil with air-gap) can be placed parallel to the primary Winding of said line signal transformer, as shown in Fig. 1, (40).

According to another feature of the invention provision is made for eliminating the above mentioned difficulties of passing both voice and pulsating currents through the same transformer of ordinary construction by the introduction of a special line signal transformer, which can be used either alone, if its magnetic circuits comprises a material of high initial permeability and of substantially constant higher permeabilities for normal induction densities of the magnetic eld produced by said pulsating currents, or in parallel with the ordinary line voice current transformer, whereby both secondaries of said transformers are connected in parallel to the trunk line.

By this latter arrangement the transformers can be dimensioned each one for its special purpose, as otherwise the line transformer must be dimensioned for both the voice currents and the signal pulsating currents of about 800 and 10 cycles per second respectively.

If only one line transformer is used with special magnetic circuit material according to this invention, it will transmit both voice and pulsating currents equally well.

Instead of using a special line signal transformer the connection of the transmitting and receiving means to the trunk line can according to this invention be made by means of a balanced receiving relay, provided with differential windings directly connected to the line parallel to the secondary of an ordinary voice current transformer, but in this case the core of the said relay must consist of -magnetic material of high initial permeability and of low or no remanence in the same manner as in the above mentioned special line signal transformer.

A further feature of the invention relates to the generation and to the reception of definite current impulses to be transmitted in any direction ofthe line singly or simultaneously.

The transmission means preferably comprise an auxiliary signal transformer in combination with a condenser of sufficient capacity to be charged and discharged in series or in parallel with the said auxiliary signal transformer, whereby very simple transmitting circuits are obtained. On the same time the great advantage is obtained of easily transmitting current impulses of any desired direction, amplitude and voltage for various conditions and purposes.

The condenser is t'hus arranged to be charged from a current source andY discharged under control of transmitting arrangements generally in the form of two or more relays or the like, the contact combinations of which determine beforehand the'kind of signal current impulse to be transmitted. Y

The transmission means can'alternatively `consist of an auxiliary signal transformer, the primary of which'is connectable to a direct current source in` such a way that a current to pass in one or the other direction through the primary of said auxiliary'signal transformer can be established or interrupted. In the secondary of said transformer there is thus generated pulsating current signals rof any beforehand desired direction, said signals being of very short duration, which pulsating signals rare transferred either directly to the line over balanced receiving means differentially connectedto the line or are passed to -fthe-` transmitting circuits, Yfrom which the transfer to thek line takes place over special line signal transformers.

Another important feature of the invention refers to the receiving means to be coordinated with the-above mentioned transmitting means"A in order tofacilitate the passing and reception of pulsating signal? impulses of any direction and of any sequence of polarity.

According to the invention the receiving meansr comprise a polarized relay of special construction which is provided with two armatures, independent of each other, of which one armature in known way can make desiredv contact combinations in either of thel polarised operating positions. The other armature is, however, biased and' is operated when the relay isY magnetised in one direction only and then only during the short time interval that the magnetising effectV ofthe received pulsating' current impulse exists', whereafter the armature is returned to its normal position by means of a bias arrangement. Apart from the ordinary signals to be transmitted and received the relay is particularly suitable for the reception and indication ofv more special signals, for example, alarm signal or long distance indicating signals for the interruption of la local conversation in favour of a long distance conversation, etc.

The inventive ideas can, ofcourse, be variedinl a great number of ways, depending upon the transmission system in which the invention shall' be used and4 also depending upon the type .of signals thatshall be transmitted.

The invention is further described and explained in connection with the accompanying" drawings of which:

Fig. 1 represents a simplified diagram of two exchanges or stations inductively interconnected by a trunk line, complete transmitting means in one station and complete receiving means in the other station only shown. The connecting means associated with the transmitting and receiving means on each station consists of a differentially balanced line signal transformer for transmission' and reception in both directions.

Fig. 2 shows a similar arrangement as in Fig. 1, but'the connecting means to the trunk line associated with lthe transmitting and receiving means on each station consists of a line signal transformer provided with a magnetic circuit core of high initial permeability and of higher substantially uniform permeability at normal magnetising currents.

Figs. 3, 4 and 5 show different inductive connections to the trunk line at each station, said connections combined with corresponding balancing and receiving'means.

The line connection and the balancing and receiving means shown in these figures can be interchanged with corresponding means shown in Fig. 1 or in Fig.l 2, depending for what purpose the signaling shall be made.

Fig. 6 shows some details of one form of signal transmission means according to the invention'- for the transmission of a plurality of" signal impulses in any direction.

Fig. 7 is a simplified diagram of a four-wire trunk line for two physicaland one phantom' circuits. Connecting means and part of receiving and balancing means are shown at each station. The receiving and transmitting means of each circuit and on each station are otherwise the same as` those shown in Fig. 1.

In Fig. 1 are stations A and B two terminal telephone exchanges united bya two-wire trunk ^f` line; 'The trunk line is Vinductively connected to` transformer AT3. AI is the line relay of a telephone station connected to exchange A, which relay repeats the impulses of the dial of said telephone station. AIZ is a relay to change the direction of a transmitted signal impulse. A3 is a slow acting relay to be energised during each train of impulses from relay AI. A6 and AII are part of the receiving equipment which is more completely shown on exchange B where B6 and BI I correspond to relays A6 and AI I.

AIU is a polarised relay with winding 3| and provided with a biased armature 2 with break and make contacts I and 3. AID is further provided with a second armature 5, following the polarity of the relay and provided with a make and break contact. BIZ, B6, BII and BID correspond to AIZ, A6, AII and AID. BI3, BI5 and B4 are used exclusively for the reception of signals on station B. ATI is a voice current transformer with primary windings 52 and 53 separated by condenser 5| and secondary windings 48 and 49 separated by condenser 5I). The condensers 50 and 5I serve the purpose of preventing pulsating current impulses to be transmitted over said voice current transformer. ATZ is a line signal transformer the secondary of which is connected to the line in parallel with the secondary of the voice transformer ATI. The secondary of ATZ is provided with four balanced windings 33, 34 and 35, 3B. Between windings 34 and 35 there is connected a balancing network 54. The primary 32 of ATZ is connected in series with winding 3l of the polarsed receiving relay AIO.

Transformer AT3 is an auxiliary signal transformer, the secondary of which is provided with two balanced differential windings 37 and 38, connected to the center points of the also balanced, differential, secondary windings 33, 34 and 35, 36 of the line signal transformer ATZ. The center point of the secondary winding ci auxiliary transformer ATS can be used for phantom line connection, as shown in Fig, '7. The primary 39 of AT3 is connected to the transmitting means, which will be further described with reference to Fig. 6.V 40 is an inductance used as balancing means; 4I is an inductance in series with the transmitting circuit and condenser 43 and resistance 4Z are connected in parallel to the said transmitting circuit in order to 4form sinus-shaped pulsating current impulses, so as not to interfere with the Voice currents that may be transmitted simultaneously over the line.

Similar arrangements exist also on exchange B, where corresponding relays and transformers are provided with the prefix B. The relay contacts on each relay are numbered progressively with the same numbers. To distinguish, for instance contact spring 5 on. relay AIZ, this combination is expressed as follows: 5AI2.

The invention will Vbe better understood in connection with the following description of the operation of diagram shown in Fig'. l.

'I'he general operation will be the following: A callingrstation, connected to exchange A, desir- -ing connection over the trunk line to another ex change B, obtains, after certain connecting opv erations over known circuit arrangements not shown in the drawings, connection to the repeating relay AI, which is energized when the receiver is off the hook. Relay A3 is thereby en- Vexchange B ergized and its contacts 2 and 3 closed, whereby ground is connected to the busy-signal-wire c. When contact 2-3AI is closed, the condenser 44 is charged in series with primary Winding 39 of auxiliary signal transformer AT3 over the following circuit: Ground, contact 3-ZAI, condenser 44, contact 3-4AI2, choke 4I, primary 39 and battery 30.

in the secondary 31-38 of AT3 is hereby induced a voltage, causing a signal current impulse in series with windings 33 and 35 of line signal transformer ATZ and the line. This signal causes a call on the receiving exchange B, which is provided with corresponding transmitting means as on exchange A, although not completely shown in the drawing. Exchange B is, however, provided with complete receiving means. The above mentioned current impulse on the line passes over both line branches in series and also in series with all windings 33', 34', 35', 36' of line signal transformer BTZ.

This current impulse causes another impulse in the primary winding 32 of said line signal transformer, which current impulse causes the polarised relay 3|' to close its contacts Z-3 and 5 6, of which the armature and contact spring Z is biased, returning immediately to its normal position with closed Contact I-2, The contact 2-3 was thus only momentarily closed during the duration of the current impulse only, while the other armature and spring 5 remains in contact with contact IS also after ceasing of said current impulse, or until a current impulse of opposits direction arrives.

Relay BI I is thereby energized over the following circuit: Ground, contact -GBIIL winding BE I, battery. Contacts 3-4BII and i-ZBI are closed. Slow-acting relay B6 is energised and its contacts I-2B6 and 3-4B8 are closed, causing in turn slow-acting relay B4 also to energise, as soon as Contact 4-5BIO is closed by impulsing.

Contact I-ZBII repeats the impulse in the in known manner over contact i-2B6, winding B5, a', knownconnecting organs, not shown, b. When the impulse ceases the following relays are in said moment energised: AI, A3, B6 and BIL Polarised relay BIO has then its contacts i--Z and 5 6 closed.

If a series of impulses now shall be transu acting Vand. remains energised as long as the calling station is connected to the repeater.

At the beginning of each impulse the contact l-ZAI is closed, and at the end of each impulse contactZ-3AI is closed.

Hereby the condenser 44 is discharged and charged respectively in series with primary winding 39 of the auxiliary transformer ATS, whereby voltages of each other opposed polarities are induced in secondary windings 3l and 38 of said transformer ATB. These voltages cause pulsatingcurrents of each other opposed directions, which are transmitted over the line.

At the exchange B these pulsating current impulses are received by all the secondary windings 332-36 in series. Relay B55 hereby receives pulsating current impulses from the primary 32 of said transformer BTZ, which pulsating currents cause contact S--EBID to be interrupted at the beginning of each impulse and the contacts 2*-3 and 5-6BIO to be closed at the end of each momentarily (biased as mentioned above).

impulse, whereby contact 2-3Bl0 is only closed In this manner relay BH follows exactly the movements of relay Ai on exchange A. The relays B6 and B4 operate in known manner as slow-acting blocking-relays, and pulsating impulses and series of such impulses are retransmitted to oonductors d and b Awith contact l-EBII as impulse-contact.

When at the called station the receiver is lifted off its hook, a call-counting-signal is transmitted from. the called :exchange back to the calling exchange in the following Way: When the called station answers, relay B is energized according known manner, Relay AI2 can be used for sending a special impulse tothe called exchange in order to interrupt a local conversation and establish a long distance connection instead, as long-distance calls should have preference to local calls.

When at the called station of exchange B the receiver is returned to its hook a pulsating clearing signal is transmitted over the line in opposite direction to the signal transmitted when the receiver was lifted from its hook. Said pulsating clearing signal is transmitted in the following Way: When the receiver is replaced on its hook at station B relay B5 is deenergised, contacts 2`3B5 being closed. The condenser 44 which was earlier charged is now discharged upon being shortcircuited, both its plates being connected to the same battery pole. An impulse is than transmitted in opposite direction from B to A and said impulse is received at A by relay AIG in similar way as above described. Relay AIG opens its contacts -J, whereby relays AI I and A6 are de-energised. A6 is de-energised and closes its contact l-ZAES, whereby the holding circuit on `the c-wire to battery 30 is closed. The holding connections in the automatic exchange A is herebytripped in known way and all relays are returned to normal as soon as the calling party also replaces his receiver on its hook, whereby relays A! and A3 also return to normal.

From the` above description it is realised that signals can be sent in one or the other direction,

and which signals even can be sent simultane ously without in any way interfering with each other. By this system there is accordingly no chanceof relays or switches or trunk lines being blocked, as has often been the case heretofore, but the signals can be transmitted freely as if direct metallic connection existed between the exchanges.

The junction, trunk or long distance lines can thus be occupied only during the time indispensable for each conversation and will afterwards be free for new connections.

The invention makes economically possible the `phantomisation of'even relatively short junction lines between central exchanges in the same city, thereby increasing trunking facilities without the outlay of large fresh capital for new trunk cables. The existing junction cable plant can thus be increased 50% without new cables being laid. The insignificant outlay for transformers and relays at each exchange according to the invention is only a fraction of the cost of new cables. The longer the lines the more economical will be the application of the invention and for long distance lines new vistas are opened up for direct and automatic establishment of connections between stations in for'instance automatic `telephone exchanges located incities far apart and without the intervention of long-distance operators.

' Fig. 2 is a similar arrangement to that shownv in Fig. v1,1the transmitting and receiving means being principally the same. The connecting and balancing means are, however, somewhatdifferently arranged. The auxiliary transformers AT3 and BT3 are here omitted. The line signal 4transformers ATfi and BTl have their secondaries `nected to the exterior windings 5@ and 59, while between the middle windings t? and 58 a bal- .ancing network is connected.

The transmitting circuit is differentially connected to these balanced windings in the follow-l ingmanner: Choke coil 4l in the transmitting circuit is connected to the center point between windings- 55 and 5l, while the center point between windings 58 and 59 is connected to battery 30. The balancing means are similarly connected to the transmitting circuits at exchange B.

The line signal transformers ATll and BT4 .are provided with cores 53 and S3 of magnetic material of i high initial permeability and of a higher substantially uniform permeability for the magnetic field and magnetising forces used in the range of transmitted signal currents. The remanentinagnetism will under these conditions be Ynegligible and the inductance substantially constant, wherefore a perfect balance vwill be obtained, so that interference between transmitted and received signals cannot be noticed in any way.

The'transmitting means are completely shown in exchange A while in exchange B only part of the complete transmission means are shown.

Similarly receiving means are completely shown in exchange B, while only part of the receiving means are shown in exchange A. This i Way of showing the circuits has been resorted to for the sake of clarity.

The operation is very similar to that described in Fig. 1.

*Figs 3, 4 and 5 show different ways of connecting the receiving and transmitting means in a balanced way to a trunk line and are interconnectable to the transmitting and receiving circuits 'shown in Fig. 1 or Fig. 2. Same numbers indifferent figures refer to same devices.

Fig. 6 is a diagrammatic detail of the transmit ting arrangement used according to this invention, whereby in a very simple way pulsating curpulses can be sent over the inductively connected line.

AT5 is a line signal transformer by means of which pulsating current impulses are transmitted to the line. 'I'he transformer should preferably be a step-up transformer, because in this way lower initial voltage can be used on the condenser 44, which preferably should be of the electro'lytic type so .as to have large capacity at a reasonable price. In this way existing batteries can be used even if they are of low voltage. It is therefore entirely feasible by means of a suitable line-transformer and a condenser to obtain current impulses of 100 or 200 volts even if a battery of only 3 to 6 volts should be available.

66 and 61 are relays connected to electric circuits of remote control, which relays operate its respective contact spring groups, as will be here shown. Instead of relays 66 and 6l the contact spring sets can of course be selectively operated in any other way, for instance by telegraph keys, mechanical switches and the like. 4I is a choke arranged to lter out not desired harmonics, which eventually could be generated in the condenser circuit. 44 is the said condenser and 45 is an ohmic resistance for the discharge of the condenser 44.

The device operates in the following Way: When Contact 69-10 is closed, the condenser 44 is rapidly charged in series with the primary E4 of the line signal transformer AT5, whereby a current impulse, which with respect to its direction may be called positive, is transmitted over the line connected to the secondary winding 65 of AT5. The line is provided at its other end with receiving means to receive the transmitted current impulses, for instance, electromagnetic relays, etc. When contacts 68-59 again are closed, the condenser is caused to be discharged, which performance causes a new current impulse, but now of negative direction over the line.

The two transmitted impulses can either together form a certain signal or can form two different signals, which on the receiving side can be received by, for instance, a polarised relay or the like as previously related.

The arrangement shown in Fig. 6 can, however, also be used for the transmission of two consecutive impulses of the same direction instead of alternatively positive and negative. supposing, thus, that contact 69--10 is closed, which means that a positive pulsating signal previously has been transmitted according to the following circuit: Ground, contact 1U--69, condenser 44, contact I3-J4, choke 4|, primary winding 64, battery 30. Hereby a positive current impulse has been generated in the secondary winding of the transformed AT5 and transmitted over the line. If the contacts I4-J5 and '1I-12 now are caused to be closed by one way or the other, the condenser 44 will be discharged over the resistance 45 and no negative current impulse will thereby be transmitted to the transformer or the line.

If thereafter contact 'l I--T2 is opened and contact 13-14 is closed in here mentioned order, the condenser 44 is again charged in series with the primary of the transformer AT5, whereby another positive pulsating signal will be transmitted over the line. By means of the contact combinations II-12, M -'l5 and 13-14 of relay 61 or the like any number of positive current impulses can be transmitted, provided contact 59-10 of relay 66 is closed.

If only pulsating negative impulses are desired on the line these can be generated in similar ways.

In Fig. 7 is shown a phantom circuit established over two physical lines, all circuits equipped for the transmission of impulses according to the invention.

The same arrangement as shown in Fig. 1 with respect to the transmitting, receiving, balancing and connecting means is used in Fig. '7 for both physical and phantom circuits. The transmission contacts l, 2 and 3 are the same as shown on relay A! and operate in the same way as on said relay, the relay windings not having been shown in order to avoid crowding of the drawings.

Fig. 7 as an example of transmitting pulsating currents over side and phantom circuits should be read in combination with Fig. l.

What we claim is:

1. In a transmitting system comprising the simultaneous transmission of signals in both directions over a trunk line by means of pulsating currents of any desired sequence of polarity, two stations, each thereof comprising a direct current source, transmitting and receiving means, connecting means permanently and inductively connecting said stations and said transmitting and receiving means to said trunk line, balancing means associated with said transmitting, receiving and connecting means, said balancing and connecting means being of such a magnetic constitution and electrically so connected that their magnetic and electrical characteristics remain substantially constant at any normally transmitted current magnitude at any of the stations.

2. The system claimed in claim 1, comprising the transmission of signals and of voice currents between two telephone exchanges, each thereof comprising a line transformer for voice and high frequency currents inductively connecting said exchanges to the trunk line and a line signal transformer connecting said transmitting and receiving means to the trunk line, both secondaries of said transformers being connected in parallel to the said trunk line.

3. The system claimed in claim 1, comprising the transmission of signals and of voice currents between two telephone exchanges, each thereof comprising a line transformer for voice and high frequency currents inductively connecting said exchange to the trunk line and a line signal transformer connecting said transmitting and receiving means to the trunk line, both secondaries of said transformers being connected in parallel to the said trunk line, the secondary of the line signal transformer being divided in two equal parts, interconnected by a network, the center point of each such part being connected to the transmitting circuits so that the ampere wind ings of the two parts of each pair cause magnetic fields of opposite direction when signal currents from the same station are transmitted through said line signal transformer.

Il. The system claimed in claim 1, comprising the transmission of signals and of voice currents between two telephone exchanges, each thereof comprising a line transformer for voice and high frequency currents inductively connecting said exchanges to the trunk line, a line signal transformer connecting said transmitting and receiving means to the trunk line, both secondaries of said transformers being connected in parallel to the trunk line, the secondary of the line signal transformer being divided in two equal parts, interconnected by a balancing network, the center point of each such part being connected to the transmitting circuits so that the-ampere windngsof the two parts of each pair causemagnetic fields of opposite direction Whensignal 'currents frein the same-"station Iare transmitted through saidline signal transformer', and an auxiliary signal transformer,`the primary of which being connected tothe transmission circuits and the secondary of whici'ibeing connected over the said center* points ofi-said half-windings of the said line signal transformer to the trunk line.

5. The system claimed in claim l, in which the transmitting means comprises a special signal transformer, the secondary of which is connected to the trunk line over which the pulsating current signals are to be transmitted and a condenser to be charged and/or discharged by means of currents from said direct current source through the primary of said signal transformer.

6. The system claimed in claim 1, in which the transmitting means comprise a special signal transformer, the secondary of which is connected to the trunk line, over which the pulsating current signals are to be transmitted and a condenser to be charged and/or discharged by means of current impulses from said current source through the primary of said signal transformer, one side of said primary connected to one pole of the direct current source and the other side connected in series with one side of the condenser, the other side of said condenser being connectable to either of the poles of said current source by means of a pole changing transmitting device.

7. The system claimed in claim, 1, in which the transmitting means comprises a special signal transformer the secondary of Which is connected to the trunk line over which the pulsating current signals are to be transmitted and a condenser to be charged and/or discharged by means of current impulses from a current source through the primary of said signal transformer, one side of said primary connected to one pole of said direct current source and the other side connected in series with an interrupting and shortcircuiting device of said primary which is further connected in series with one side of the condenser, the other side of said condenser being connectable to either of the poles of said current source by means of a pole changing transmitting device.

8. The system claimed in claim 1, in which the transmitting means comprise a special signal transformer, the secondary of which is connected to the trunk line over which the pulsating current signals are to be transmitted and a condenser, one side of which being connectable to either of the poles of said current source by means of a pole changing transmitting device and the other side of said condenser being convnectable in series with an interrupting and shortcircuiting device of said condenser to the primary winding of said signal transformer, whereby the condenser can be charged and/or discharged.

9. 'I'he system claimed in claim 1, in which the transmitting means comprise a special line signal transformer, the secondary of which is connected to the trunk line over which the pulsating current signals are to be transmitted, and a condenser, one side of which being connectable to either of the poles of said current source by means of a pole changing transmitting device and the other side of the said condenser being connectable in series with an interrupting and short-circuiting device of said condenser and 'in series with a choke coil to the primary -windthe said connecting means comprise a `special vlineftransform'er associated `with said balancing means and with said transmitting and receiving means, the magnetic circuit of said line transformer comprising a magnetic circuit material of high initial permeability and of relatively constant higher permeabilities for normal induction densities of the magnetic iield produced by said pulsating currents, whereby a substantially constant inductance of the said line transformer is maintained for any normally transmitted current signal magnitude l1. The system claimed in claim 1, in which the said connecting means comprise a special line transformer associated with said balancing means and with said transmitting and receiving means, the magnetic circuit of the said line transformer comprising a magnetic material of a high initial and relatively constant permeability for normal induction densities of the magnetic eld produced by said pulsating currents, the secondary of said line transformer being connected to the trunk line, and in which the receiving means comprise a relay provided with two pairs of windings, the outside end of a winding of each pair interconnecting the primary of said line transformer, the interior end of a winding of each pair interconnecting a balancing network, and in which the transmitting means comprise a condenser to be charged and/ or discharged by means of currents from said current source, the condenser being differentially connected to the center points of said pair of windings', so that the transmitting current signals from said condenser can pass differentially over said windings to the primary of the line transformer without operating the armature of said receiving relay.

12. In a transmitting system comprising the simultaneous transmission of signals in both directions over a trunk line by means of pulsating currents of any desired sequence of polarity, two stations, each thereof comprising a direct current source, transmitting and receiving means, connecting means permanently and inductively connecting said stations and said transmitting and receiving means to said trunk line and balancing means associated with said transmitting and receiving means to impede interference between transmitted and received signals at any normally transmitted current magnitude at any of the stations, said receiving means comprising a polarized relay of a number oi' contact combinations of which at least one of them is provided With a biased contact spring arranged to be momentarily operated during such length of time a momentary current impulse is being received in one direction over the trunk line only.

13. The system claimed in claim 12, in which said polarized relay is provided With two armatures, one of them provided with a make and break contact combination to be definitely operated by received polarized momentary current impulses, the other armature being provided with a make and break contact combination, its make contact to be momentarily closed during such length of time a momentary current impulse is being received in one direction over the trunk line only, said armature by means of a biased contact spring being returnable to its normal break Contact position immediately upon ceasing of the said current impulse.

14. In a transmitting system for transmission of signals over a trunk line by means of pulsating direct currents of any desired sequence of polarity, a direct current source, transmitting means, a signal transformer, the secondary of said transformer permanently and inductively connecting said transmitting means to said trunk line, said transmitting means comprising a condenser to be charged and discharged through the primary of said signal transformer by the 5 currents from said direct current source.

KARL HARRY THUNELL. STEN DANIEL VIGREN. PER HARRY ELIAS CLAESSON. 

